Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
Adenomas are benign tumours, or neoplasms, of epithelial origin which are derived from glandular tissue or exhibit clearly defined glandular structures. Some adenomas show recognisable tissue elements, such as fibrous tissue (fibroadenomas) and epithelial structure, while others, such as bronchial adenomas, produce active compounds that might give rise to clinical syndromes.
Adenomas may progress to become an invasive neoplasm and are then termed adenocarcinomas. Accordingly, adenocarcinomas are defined as malignant epithelial tumours arising from glandular structures, which are constituent parts of many organs of the body. The term adenocarcinoma is also applied to tumours showing a glandular growth pattern. These tumours may be sub-classified according to the substances that they produce, for example mucus secreting and serous adenocarcinomas, or to the microscopic arrangement of their cells into patterns, for example papillary and follicular adenocarcinomas. These carcinomas may be solid or cystic (cystadenocarcinomas). Each organ may produce tumours showing a variety of histological types, for example the ovary may produce both mucinous and cystadenocarcinoma.
Adenomas in different organs behave differently. In general, the overall chance of carcinoma being present within an adenoma (i.e. a focus of cancer having developed within a benign lesion) is approximately 5%. However, this is related to size of an adenoma. For instance, in the large bowel (colon and rectum specifically) occurrence of a cancer within an adenoma is rare in adenomas of less than 1 centimeter. Such a development is estimated at 40 to 50% in adenomas which are greater than 4 centimeters and show certain histopathological change such as villous change, or high grade dysplasia. Adenomas with higher degrees of dysplasia have a higher incidence of carcinoma. In any given colorectal adenoma, the predictors of the presence of cancer now or the future occurrence of cancer in the organ include size (especially greater than 9 mm) degree of change from tubular to villous morphology, presence of high grade dysplasia and the morphological change described as “serrated adenoma”. In any given individual, the additional features of increasing age, familial occurrence of colorectal adenoma or cancer, male gender or multiplicity of adenomas, predict a future increased risk for cancer in the organ—so-called risk factors for cancer. Except for the presence of adenomas and its size, none of these is objectively defined and all those other than number and size are subject to observer error and to confusion as to precise definition of the feature in question. Because such factors can be difficult to assess and define, their value as predictors of current or future risk for cancer is imprecise.
Once a sporadic adenoma has developed, the chance of a new adenoma occurring is approximately 30% within 26 months.
Colorectal adenomas represent a class of adenomas which are exhibiting an increasing incidence, particularly in more affluent countries. The causes of adenoma, and of progression to adenocarcinoma, are still the subject of intensive research. To date it has been speculated that in addition to genetic predisposition, environmental factors (such as diet) play a role in the development of this condition. Most studies indicate that the relevant environmental factors relate to high dietary fat, low fibre, low vegetable intake, smoking, obesity, physical inactivity and high refined carbohydrates.
Colonic adenomas are localised areas of dysplastic epithelium which initially involve just one or several crypts and may not protrude from the surface, but with increased growth in size, usually resulting from an imbalance in proliferation and/or apoptosis, they may protrude. Adenomas can be classified in several ways. One is by their gross appearance and the major descriptors include degrees of protrusion: flat sessile (i.e. protruding but without a distinct stalk) or pedunculated (i.e. having a stalk). Other gross descriptors include actual size in the largest dimension and actual number in the colon/rectum. While small adenomas (less than say 5 or 10 millimeters) exhibit a smooth tan surface, pedunculated and especially larger adenomas tend to have a cobblestone or lobulated red-brown surface. Larger sessile adenomas may exhibit a more delicate villous surface. Another set of descriptors include the histopathological classification; the prime descriptors of clinical value include degree of dysplasia (low or high), whether or not a focus of invasive cancer is present, degree of change from tubular gland formation to villous gland formation (hence classification is tubular, villous or tubulovillous), presence of admixed hyperplastic change and of so-called “serrated” adenomas and its subgroups. Adenomas can be situated at any site in the colon and/or rectum although they tend to be more common in the rectum and distal colon. All of these descriptors, with the exception of number and size, are relatively subjective and subject to interobserver disagreement.
The various descriptive features of adenomas are of value not just to ascertain the neoplastic status of any given adenomas when detected, but also to predict a person's future risk of developing colorectal adenomas or cancer. Those features of an adenoma or number of adenomas in an individual that point to an increased future risk for cancer or recurrence of new adenomas include: size of the largest adenoma (especially 10 mm or larger), degree of villous change (especially at least 25% such change and particularly 100% such change), high grade dysplasia, number (3 or more of any size or histological status) or presence of serrated adenoma features. None except size or number is objective and all are relatively subjective and subject to interobserver disagreement. These predictors of risk for future neoplasia (hence “risk”) are vital in practice because they are used to determine the rate and need for and frequency of future colonoscopic surveillance. More accurate risk classification might thus reduce workload of colonoscopy, make it more cost-effective and reduce the risk of complications from unnecessary procedures.
Adenomas are generally asymptomatic, therefore rendering difficult their diagnosis and treatment at a stage prior to when they might develop invasive characteristics and so became cancer. It is technically impossible to predict the presence or absence of carcinoma based on the gross appearance of adenomas, although larger adenomas are more likely to show a region of malignant change than are smaller adenomas. Sessile adenomas exhibit a higher incidence of malignancy than pedunculated adenomas of the same size. Some adenomas result in blood loss which might be observed or detectable in the stools; while sometimes visible by eye, it is often, when it occurs, microscopic or “occult”. Larger adenomas tend to bleed more than smaller adenomas. However, since blood in the stool, whether overt or occult, can also be indicative of non-adenomatous conditions, the accurate diagnosis of adenoma is rendered difficult without the application of highly invasive procedures such as colonoscopy combined with tissue acquisition by either removal (i.e. polypectomy) or biopsy and subsequent histopathological analysis.
Accordingly, there is an on-going need to elucidate the causes of adenoma and to develop more informative diagnostic protocols or aids to diagnosis that enable one to direct colonoscopy at people more likely to have adenomas. These adenomas may be high risk, advanced or neither of these. Furthermore, it can be difficult after colonoscopy to be certain that all adenomas have been removed, especially in a person who has had multiple adenomas. An accurate screening test may minimise the need to undertake an early second colonoscopy to ensure that the colon has been cleared of neoplasms. Accordingly, the identification of molecular markers for adenomas would provide means for understanding the cause of adenomas and cancer, improving diagnosis of adenomas including development of useful screening tests, elucidating the histological stage of an adenoma, characterising a patient's future risk for colorectal neoplasia on the basis of the molecular state of an adenoma and facilitating treatment of adenomas.
To date, research has focused on the identification of gene mutations which lead to the development of colorectal neoplasms. In work leading up to the present invention, however, it has been determined that changes in expression profiles of genes which may also expressed in healthy individuals are indicative of the development of neoplasms of the large intestine, such as adenomas and adenocarcinomas. More specifically, there has been identified a gene, an increase in the expression of which is indicative of the onset of a large intestine adenoma or adenocarcinoma. Yet more particularly, it has been determined that this gene, which comprises SEQ ID NO:1 and is herein called hCG_1815491, encodes 18 identified exon segments, several of which are expressed in two or more splice variants forms. hCG_1815491 has now been found to transcribe to at least 11 variant RNA transcript forms. It has still further been determined that although the levels of multiple transcribed forms of hCG_1815491 show some level of increase in expression in the context of neoplasia development, hCG_1815491 is, in fact, alternatively spliced in a neoplastic specific manner, thereby enabling a level of diagnostic and prognostic discrimination which is rarely available in the context of a single gene and has been unavailable in terms of the diagnosis of colorectal neoplasias. The findings of the present invention have therefore facilitated the development of a screening method to diagnose the onset, or predisposition thereto, of adenocarcinoma, adenoma and/or the monitoring of conditions characterised by the development of these types of neoplasms.